Strength 4 ap 5 isn't something to scoff at. Kills anything that isn't a fellow power armored guy or has a 4+ save (Which to be honest I don't see much of, the 4+ save that is)
Dual wield bolt/plasma pistols for range and dual wield force swords for the fun stuff. Never gonna happen but it would be a laugh.
Really depends what is implimented in game really, Nurgle based magic would be high on my list, Melee closely following it (or possibly ahead depending how its done) Gief Manreaper!
In space marine theirs a segment near the beginning where there's a bunch of guardsmen with lasguns firing at the orks and you have to save the guards. If you just watch the guards fight they take forever to kill any orks. Not to mention that fluff wise space marine messed up in many details in this respect at least it was fairly accurate of lasguns doing jack and then you put one bolt pistol round through the head and you kill an Ork. Dawn of War is a strategy game and thus, BALANCE = FUN and Fun>lore accuracy. I have, I'm just saying that the bolter isn't garbage and if anything is the measuring tool to place all other weapons against.
NPC's are always useless plebs. Now I'm not the sort of idiot who'll talk down mass reactive shells lore wise and hell if Bolters in EC give me half the raging murder-erection I recieved from blowing apart anything that walked in Fire Warrior then I know I'll be lootin' one first chance I get. All I'm saying is games have historically not done well with them and that they haven't got enough Dakka to make this Ork chuckle.